This section provides background information related to the present disclosure which is not necessarily prior art.
Conventional spark plugs for use in internal combustion engines generally include metal shell housing, a ceramic insulator, a center electrode, and a ground electrode. The shell housing has a threaded portion for locating an end portion of the spark plug in a combustion chamber of the engine. The insulator is fixed in the shell housing such that an end of the insulator protrudes from an end of the shell housing. The center electrode is secured in a center bore of the insulator such that a tip end of the center electrode protrudes from the end of the insulator. The ground electrode is fixed to the shell housing and has a side surface that is opposed to and spaced from the tip end of the center electrode so as to form a spark gap therebetween. By applying a high voltage across the center electrode and the ground electrode, a spark discharge takes place within the spark gap, thereby igniting the air-fuel mixture within the combustion chamber.
Spark plug technology for gasoline engines continues to develop in an effort to promote higher performance and longer service life. Following this trend, gasoline engines have also continued to develop as fuel economy and emission standards have advanced. As a result, lean burn engines now create higher combustion chamber temperatures which can directly influence spark plug performance, specifically ignitability and heat dispersion away from the ground electrode. To avoid engine damage from pre-ignition events and alleviate durability concerns, it is known that combustion chamber temperatures exceeding the ground electrode threshold must be kept to a minimum.
In an effort to address these concerns, “shrouded” spark plugs have been used in some severe engine environments to assist in dissipating heat away from the ground electrode. The concept of a shroud-type spark plug is based upon joining a shortened ground electrode to a cylindrical collar that is fixed to the shell housing and configured to completely surround the center electrode as well as some or all of the ground electrode. This shrouded shell housing configuration creates higher heat conductivity which promotes quicker heat mass transfer to the shell housing and away from the ground electrode. While shroud-type spark plugs assist in promoting improved cooling of the ground electrode, they have a negative effect on the optimal tumble pattern for the air-fuel mixture around and within the sparking area which can result in lower ignitability and less complete combustion.
Accordingly, as engine technology continues to advance, a need exists to continue development of advanced spark plug technologies directed to improved heat dissipation from the ground electrode while maintaining high ignitability for a complete burn and ensuring a long service life.